Pass paramater from DropDownList to Stored Procedure

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C#

ASP.NET

Hi, I want to create a dropdownlist when an item is selected the user is redirected to another page and content about the item is displayed, all of this is done with stored procedures, but it does not seem to pass parameters to the stored procedure. I know the paramater is not passing but I don't know ehy not.
error:
Procedure or Function 'GetWidth' expects parameter '@WidthID', which was not supplied.
Can anyone help please?

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string widthId =
            Server.UrlEncode(form.SelectedValue.ToString());
       
        Response.Redirect(Link.ToWidth(widthId));
    }

private static string BuildAbsolute(string relativeUri)
    {
            // get current uri
        Uri uri = HttpContext.Current.Request.Url;
            // build absolute path
        string app = HttpContext.Current.Request.ApplicationPath;
        if (!app.EndsWith("/")) app += "/";
        relativeUri = relativeUri.TrimStart('/');
            // return the absolute path
        return HttpUtility.UrlPathEncode(
            String.Format("http://{0}:{1}{2}{3}",
            uri.Host, uri.Port, app, relativeUri));
    }
        // generate a width URL
    public static string ToWidth(string widthId)
    {
        return BuildAbsolute(String.Format("WidthAdmin.aspx?Width={0}", widthId));
    }

This is the receiving page, maybe I'm not calling it correctly, cause if I don't populate the GridView I get no errors

protected void Page_Load(object sender, EventArgs e)
    {
            // load the grid only the first time the page is loaded
        if (!Page.IsPostBack)
        {
                // load the department grid
            BindGrid();
        }
    }
        // populate the grid view with data
    private void BindGrid()
    {
        string widthId =
            Server.UrlDecode(Request.QueryString["WidthID"]);
            // get a DataTable object containing the catalog departments
        grid.DataSource = CatalogAccess.GetWidth(widthId);
            // bind the data bound controls to the data source
        grid.DataBind();
    }